Ju Min

Nitrogen Balance and Loss in a Greenhouse Vegetable System in Southeastern China

Abstract High rates of fertilizer nitrogen (N) are applied in greenhouse vegetable fields in southeastern China to maximize production; however, the N budgets of such intensive vegetable production remain to be explored. The goal of this study was to determine the annual N balance and loss in a greenhouse vegetable system of annual rotation of tomato, cucumber, and celery at five N (urea) application rates (0, 348, 522, 696, and 870 kg N ha −1 year −1 ). Total N input to the 0–50 cm soil layer ranged from 531 to 1 053 kg ha −1 , and N fertilizer was the main N source, accounting for 66%–83% of the total annual N input. In comparison, irrigation water, wet deposition, and seeds in total accounted for less than 1% of the total N input. The fertilizer N use efficiency was only 18% under the conventional application rate of 870 kg N ha −1 and decreased as the application rate increased from 522 to 870 kg N ha −1 . Apparent N losses were 196–201 kg N ha −1 , of which 71%–86% was lost by leaching at the application rates of 522–870 kg N ha −1 . Thus, leaching was the primary N loss pathway at high N application rates and the amount of N leached was proportional to the N applied during the cucumber season. Moreover, dissolved organic N accounted for 10% of the leached N, whereas NH 3 volatilization only contributed 0.1%–0.6% of the apparent N losses under the five N application rates in this greenhouse vegetable system.

Transgenic tomato overexpressing ath-miR399d has enhanced phosphorus accumulation through increased acid phosphatase and proton secretion as well as phosphate transporters

By generating and examining transgenic tomato overexpressing ath-miR399d grown in hydroponic conditions, in quartz sand, or in a polytunnel greenhouse vegetable soil culture, this study aimed to investigate the effects of miR399d from Arabidopsis on phosphorus (P) accumulation, P concentrations in transgenic tomato overexpressing ath-miR399d shoots, phosphate transporter expression, and proton secretion and acid phosphatase (APase) activity in roots. In the transgenic tomato, leaf P concentration increased significantly in an agricultural soil, and roots had higher uptake of P, as evidenced by leaf P concentrations and relative expression of the genes LePT1, LePT2, LePT4, and LePT5 in normal-P solution. Enhanced APase activity in transgenic roots and the outside medium led to superior hydrolysis of organic P, and increased proton extrusion by roots led to superior dissolution of AlPO4. Thus, besides phosphate transporters, higher APase activity and strengthened acidification in the vicinity of the roots may be important mechanisms for transgenic tomato to scavenge or acquire P in soil. These results provide new understanding of miR399-overexpressing plants that accumulate excess P in shoots.

Influences of past application rates of nitrogen and a catch crop on soil microbial communities between an intensive rotation

The aim of this study was to investigate influences of six-year past application rates of nitrogen and a catch crop, sweet corn (Zea mays L. ssp. Saccharata Sturt), on soil microbial community and diversity in a greenhouse-based intensive vegetable soil in eastern China. Soil electrical conductivity, pH, mineral nitrogen, phospholipid fatty acids (PLFA) profiles and carbon source utilization patterns under five annually past nitrogen rates (0, 348, 522, 696 and 870 kg nitrogen ha−1) were evaluated after the establishment of sweet corn during 1–1.5-month fallow period over three-year tomato/cucumber/celery rotations. The past nitrogen application rates exerted significant effects on soil electrical conductivity, pH, nitrate-nitrogen, ammonium-nitrogen and carbon source utilization patterns, but not on PLFAs profiles. The sweet corn had a significant effect on soil chemical properties, total and actinobacterial PLFAs, but not on carbon source utilization patterns. Soil electrical conductivity, nitrate-nitrogen and the total PLFAs decreased whilst soil organic carbon, pH and the actinobacterial PLFAs increased after the establishment of sweet corn. Soil microbial functional diversity from carbon source utilization patterns and actinobacterial PLFAs were greatest after the establishment of sweet corn at a 60% of the conventional nitrogen rate (i.e. 522 kg nitrogen ha−1). Soil electrical conductivity and ammonium-nitrogen were two key factors to determine carbon source utilization patterns, whilst soil pH was the key factor to determine PLFAs profiles. A combination of the catch crop sweet corn during summer fallow and a 60% of the conventional nitrogen rate is a sustainable pathway of utilizing greenhouse-based intensive vegetable soils in eastern China.

Nitrogen discharge pathways in vegetable production as non-point sources of pollution and measures to control it

Discharge of nitrogen (N) from fertilizers applied to vegetables is becoming a serious environmental problem. In a field experiment involving a celery-tomato-fallow-lettuce rotation, leaching was the primary pathway of N loss (56.1±0.4% of the total), followed, in descending order, by runoff (11.7±0.3%), N2O emissions (1.6±0.1%), and volatilization of ammonia (0.5±0.1%). Decreasing the traditional dose of N by 40% in each growth season decreased N leaching by 22.3±4.5, 39.8±6.7, 40.3±2.9 and 27.4±3.6% in celery, tomato, fallow and lettuce seasons, respectively, without any yield loss, and modifying the rotation to include a leguminous crop reduced the N leaching by 72±2, 40±3, 24±2 and 13±1% in each season, respectively, without any economic impact. These measures decreased annual N leaching by 36±4%. A combination of the eco-ditches and wetland paddy fields adjacent to the vegetable plot led to annual N removal efficiency of 73±6% in runoff.

Transgenic tomato overexpressing ath-miR399d improves growth under abiotic stress conditions

Phosphorus (P) is an essential element required for plant growth and development. Abiotic stresses, such as cold and P deficiency cause adverse effects on growth of plants, inhibit accumulation or translocation of mineral nutrients such as P, and often constrain the productivity and quality of crops. miR399 as a long-distance signal controls systemic phosphate homeostasis by modulating phosphate uptake and transport. However, overexpression of miR399 causes P toxicity and results in retarded growth. Thus, we constructed a transgenic tomato (Solanum lycopersicum L., C1), which contains foreign gene ath-miR399d under the control of rd29A promoter. In the transgenic C1 expression of the miR399d gene showed a stress-inducible pattern. Results showed that miR399d was moderately up-regulated in response to salinity and cold stresses. In soil, dry weight was enhanced in transgenic tomato under low temperature and P deficiency conditions. The transgenic tomato has potential to improve growth when it is exposed to other abiotic stresses such as salinity and drought.

Nitrogen removal from the surface runoff of a field scale greenhouse vegetable production system

Nutrient losses from greenhouse vegetable production systems may impair water quality in the Taihu Lake Region of China. We studied the characteristics of nitrogen (N) lost via runoff from greenhouse vegetable systems and strategies for minimizing N entering water bodies. A two-year experiment at a field scale was conducted to monitor N surface runoff. An eco-ditch (148 m2) and a low N input paddy field (135 kg N ha−1, 550 m2) were designed to remove N from the surface runoff of a 25 × 50 m greenhouse vegetable field. The greenhouse was not covered from late June to mid-October each year, and runoff occurred multiple times during this period. Annual total N loss in runoff from the greenhouse vegetable site was 25.3 and 33.5 kg ha−1 in 2010 and 2011, respectively. Nitrate-N was the major form of N lost in the runoff. The average runoff volume was 289 mm (varied from 221 to 357 mm), which contained 15.7 (varied from 3.3 to 39.2 mg L−1) mg L−1 total N. The eco-ditch system and the wetland paddy field (WPF) effectively reduced total N discharge; the removal rates reached 49.9% and 58.7% and the average removal capacities were 12.4 g N m−2 and 4.1 g N m−2 in 2010 and 2011, respectively. The combined system of the ecological ditch–WPF removed almost 79% total N in the runoff. Ecological ditch or paddy wetland can be a water management option available to growers in this region to economically reduce pollutants in agricultural runoff.

Biochar application mode influences nitrogen leaching and NH3 volatilization losses in a rice paddy soil irrigated with N-rich wastewater

ABSTRACT Impacts of biochar application mode on nitrogen (N) leaching, ammonia (NH3) volatilization, rice grain yield and N use efficiency (NUE) are not well understood. Therefore, a field experiment was conducted to evaluate those impacts in a rice paddy soil received 225 kg N ha−1 from either urea or N-rich wastewater. One treatment received 10 t ha−1 biochar with the basal fertilization, and the other received same total amount of biochar but split applied with the three split N applications with same ratio as N fertilizer split ratio (40%, 30% and 30%). Results showed that N leaching loads were 4.20–6.22 kg ha−1. Biochar one-time application reduced N leaching by 23.1%, and biochar split application further reduced N leaching by 32.4%. Total NH3 volatilization loss was 15.5–24.5 kg ha−1. Biochar one-time application did not influence the NH3 volatilization, but biochar split application stimulated the cumulative NH3 volatilization by 57.7%. Both biochar treatments had no influence on NUE and rice grain yield. In conclusion, biochar application mode indeed influences the N leaching and NH3 volatilization in rice paddy soils, and biochar one-time application should be recommended for reducing N leaching without increasing NH3 volatilization.

In-Season Yield Prediction of Cabbage with a Hand-Held Active Canopy Sensor

Efficient and precise yield prediction is critical to optimize cabbage yields and guide fertilizer application. A two-year field experiment was conducted to establish a yield prediction model for cabbage by using the Greenseeker hand-held optical sensor. Two cabbage cultivars (Jianbao and Pingbao) were used and Jianbao cultivar was grown for 2 consecutive seasons but Pingbao was only grown in the second season. Four chemical nitrogen application rates were implemented: 0, 80, 140, and 200 kg·N·ha−1. Normalized difference vegetation index (NDVI) was collected 20, 50, 70, 80, 90, 100, 110, 120, 130, and 140 days after transplanting (DAT). Pearson correlation analysis and regression analysis were performed to identify the relationship between the NDVI measurements and harvested yields of cabbage. NDVI measurements obtained at 110 DAT were significantly correlated to yield and explained 87–89% and 75–82% of the cabbage yield variation of Jianbao cultivar over the two-year experiment and 77–81% of the yield variability of Pingbao cultivar. Adjusting the yield prediction models with CGDD (cumulative growing degree days) could make remarkable improvement to the accuracy of the prediction model and increase the determination coefficient to 0.82, while the modification with DFP (days from transplanting when GDD > 0) values did not. The integrated exponential yield prediction equation was better than linear or quadratic functions and could accurately make in-season estimation of cabbage yields with different cultivars between years.